A now common medical procedure in eye surgery involves the complete removal of a cataracted lens from a human eye to be later replaced with an intraocular artificial lens. The known procedure includes making an incision in the cornea. To minimize patient trauma and unnecessary tissue damage, this incision is kept very small. The entire operation of disintegrating and removing the damaged natural lens tissue is performed using instruments placed through the small incision. A small vibratory instrument is used to assist in the lens tissue disintegration. The cutting tip is generally tubular and is oscillated by the instrument along its axis at a very high frequency. The cutting tip is inserted into the incision and maneuvered by the surgeon throughout accessible portions of the capsular bag containing the natural lens. The movement of the vibrating cutting tip causes the lens tissue to disintegrate. As the lens breaks apart, the resulting loose lens particles are aspirated from the capsular bag under vacuum by way a first conduit in the tubular cutting tip of the vibrating instrument.
U.S. Pat. No. 3,589,363 to Banko and Kelman discloses such a hand held instrument for breaking apart and removing tissue from a body site, such as cataracted lens tissue from a human eye. The content of U.S. Pat. No. 3,589,363 hereby incorporated by reference.
There are several problems encountered by surgeons using the above procedure. A first problem is that in addition to the incision in the cornea a substantial portion of the anterior wall of the capsular bag must be removed, in order for the straight end of the tip to have at least some maneuverability in the capsular bag, since an intermediate portion of the tip is essentially fixed in space by its extending through the small corneal incision spaced from the capsular bag. Even after such removal, however, of the anterior capsular wall the geometry of the eye and the location of the incision restrict the accessibility of the surgeon's operating instruments within the capsular bag. In other words, the typically straight cutting tips of the vibratory instrument cannot easily be maneuvered within the capsular bag to effectively reach all parts of the lens to be removed. The straight tips may be angled slightly from side to side, but cannot be angled sufficiently to allow the working end of the tip to reach the areas at the peripheral interior regions of the capsular bag, at least not without removal of a substantial portion of the anterior capsular wall.
To overcome this accessibility problem with the known cutting tips, cutting tips have been made with varying bends, up to 90 arc-degree bends, so that the cutting tip may be maneuvered to reach additional parts of the posterior cavity while operating through the pair of spaced incisions. This bent cutting tip feature is disclosed in my U.S. Pat. No. 5,154,694, the content of which is incorporated herein by reference. Other improvements to cutting tips with less than 90 arc-degree bends are shown in my co-pending applications, Ser. No. 07/958,651, filed Oct. 8, 1992, entitled CAVITATION-GENERATING TIP FOR DISINTEGRATING TISSUE, and Ser. No. 08/055,213, filed Apr. 28, 1993, entitled BENT PHACO-TIP WITH SAFETY EDGES.
Even with these bent tips, however, the regions at the outermost peripheral portion at the interior of the capsular bag are not readily accessible to the tip without substantial opening of the anterior capsular wall. Where it is desired to minimize the opening in the anterior capsular wall, a further improved cutting tip is required.
It has been determined by the applicant that the disintegration of tissue in the immediate vicinity of the cutting tip is enhanced by the cavitation effect resulting from the ultrasonic oscillation of the cutting tip within the liquid filled environment of the capsular bag, i.e., posterior capsule.
Whenever any object having a distinct frontal surface area, with respect to the direction of movement, moves relatively quickly within a fluid, a low pressure region (i.e., negative pressure relative to the surrounding fluid) is developed just behind, or adjacent to, such frontal surface. If the magnitude of the negative pressure developed within the low pressure region becomes greater than the negative pressure required to vaporize the particular fluid, the fluid will be vaporized, creating bubbles called cavitation bubbles.
Thus, when the cutting tip of the above-described vibratory instrument moves in a direction away from the surface of the tissue to be disintegrated, a sudden low pressure region is developed within the adjacent fluid resulting in the formation of cavitation bubbles, It is believed that during each ultrasonic oscillation, as the cutting tip continues to move away from the tissue surface, the pressure in the expanding newly formed cavitation bubbles decreases. It is further believed that when the point is reached, during the cycle, where the fluid pressure outside the bubble exceeds the pressure in the expanding cavitation bubbles, there results a collapse of the cavitation bubbles and they are quickly re-absorbed into the fluid. The pressure waves in the fluid resulting from the substantially simultaneous collapsing of thousands of such tiny bubbles, operate on the nearby tissue to help disintegrate it. The rate of "collapse" of the cavitation bubbles determines the degree of assistance to disintegrating the nearby tissue. The greater the number of cavitation bubbles formed and the quicker the rate of collapse of the bubbles, the greater will be the desired damage to the nearby tissue.
It is an object of the invention to provide a cutting tip for use with a vibratory instrument which will provide even greater accessibility to previously inaccessible tissue and to provide at least one additional surface to produce the cavitation bubbles.
It is another object of the invention to provide a cutting tip that causes the disintegrated material to be drawn to the tip end, thus exposing the remaining tissue ultrasonic disintegration.
It is a further object of the invention to provide a cutting tip which will provide the maximum cavitation bubbles to more effectively disintegrate the tissue.
It is a concomitant object of the invention to provide a cutting tip which is so shaped that forwardly and rearwardly facing portions will generate cavitation bubbles for softening or for disintegration of tissue lying forwardly and rearwardly of the tip while the tip end also generates cavitation bubbles for disintegrating tissue lying rearwardly of the tip.